18% grey and metering

Discussion in 'Photography Beginners' Forum' started by gabrielh, Dec 16, 2008.

  1. gabrielh

    gabrielh TPF Noob!

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    Hello all,
    Just wanted to be sure about this: if I point the camera (say, in spot metering mode) to a white wall, then it will be metered for 18% grey and will come out as 18% grey if I don't adjust settings. This is right, isn't it? Also, I have read that if you wanted to take some portrait, just meter the brightest part of the persons face, and then increase the exposure by two stops so the white truly comes out as white and not as grey. But that seems quit a lot for me... Anybody help please?
    Thanks!
    G.
     
  2. dxqcanada

    dxqcanada Been spending a lot of time on here!

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    Yes, it will be 18% grey.
    Always handy to have a small Grey Card (I have one in my camera bag).

    Not sure about the second part ... I do not do portraits.
     
  3. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

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    All meters are designed to read a middle grey, but the actual percentage varies slightly. If you point your camera at a bright, white wall and meter it, the camera reads it as if it were a middle grey wall, and will thus over-expose the image. The resulting wall colour will be darker and muddier, but not necessarily 18% grey. With respect to your question on portraiture, I've never heard that particular piece of advice before. Two additional stops on the highlights is likely to blow out a good part of the image IMO. I would meter the scene in spot from the point which I wanted perfectly exposed (ie, if you're using a hairlight to create a "halo" you may not want to meter off of those, or if you deliberately want a good part of the face dark, don't meter from it) and use those settings to start. Take the image, review and adjust as req'd.
     
  4. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    I think you have the basic idea correct.

    If you meter off of a white wall, the camera will give you settings to expose for [18% grey]. Your wall may not come out at 18% grey in the image but it would certainly be under exposed. In this case, you would want to increase your exposure...probably between one and two stops.

    That would seem a lot to me as well...unless the brightest part of that person was pure white.

    You can essentially meter off of anything...the key is knowing how reflective that surface is and what (if any) compensation you would have to add/subtract from the meter's reading.

    The tone of most people's plam, is about one stop brighter than mid tone...so you could meter your palm and then increase exposure by one stop.

    Green foliage (grass for example) is usually about mid tone, so you could meter off of grass and use that exposure directly.

    I do think it's helpful to understand metering...but I also think that it's not nearly as important (with digital) as it was with film. Firstly, with digital you can shoot and check your exposure immediately. While it's not a great idea to use the image on the screen to accurately judge exposure, most DSLR cameras have tools to help you. Highlight tone warnings (flashing) and the histogram is great.
    Rather than careful metering, I find that I prefer to shoot, test, adjust and shoot again.

    Histogram

    Also, with digital...the 'proper exposure' may not be the 'best' exposure.
    Expose to the Right
     
  5. gabrielh

    gabrielh TPF Noob!

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    Thanks all for these fast answers! Two more questions have arrised when reading your posts:
    1. How do you use a grey card to make your exposure. Do you meter that card and you're sure you've got a "good" exposure and then adjust accordingly if the subject is black (then subtrack a stop or two) or is white (then add a stop or two)?
    2. Big Mike told about "what (if any) compensation you would have to add/subtract from the meter's reading". How do you know what compensation you have to add/subtract?
    Thanks! :D
     
  6. dxqcanada

    dxqcanada Been spending a lot of time on here!

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    Place grey card in front of subject.
    Meter off of grey card.
    Shoot.

    This is OK if the subject lighting is not extreme.

    I did this a lot when shooting moving subjects on my manual exposure camera ... also I do this with my new camera in situations where I do not want the camera playing with the auto exposure (by going manual).

    ... I used to just use my hand-held ambient light meter, until it broke.
     
  7. gabrielh

    gabrielh TPF Noob!

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    So... No adjusting for more bright or dark when using grey cards? Why nog? Why yes?
    Just wanting to learn and understand!;)
     
  8. dxqcanada

    dxqcanada Been spending a lot of time on here!

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    You meter a 18% grey card with a light meter that is balanced for 18% grey ... and you will capture grey.

    As long as the exposure latitude does not go beyond the latitude of the film/sensor ... there is no need for adjustments.

    In some extreme exposure cases you may need to shift the exposure up or down to move the highs/lows up or down to retain detail in one of those areas (and sacrificing the other).

    Ansel Adam's Zone System is a great tool to understanding exposure.
     
  9. gabrielh

    gabrielh TPF Noob!

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    Ok! Thanks dxqcanada! It sure helps!
     
  10. Jon_Are

    Jon_Are TPF Noob!

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    (jumping in here)

    So if I'm checking my histogram and 'flashing highlights' screen, and all is OK, I don't have to bother with a grey card?

    Here's where my ignorance will show: I thought the grey card metering was used to obtain correct white balance (only).

    Is it also used to obtain proper exposure?

    If I have attained proper exposure, is it a given that my white balance then is correct? Or not necessarily?

    Thanks,

    Jon
     
  11. gabrielh

    gabrielh TPF Noob!

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    Thanks Jon, for jumping in! I also knew that the grey card (I prefer a white card) was used for white balance. But I don't think the white balance is correct if the exposure is good (and vice versa). If incorrect, please correct me...
    Thanks!
     
  12. Turnerea

    Turnerea TPF Noob!

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    I'm pretty sure the typical use is a white card for WB, and a grey card for exposure. Though to be fair I don't use either.... If I need to do manual WB, I'll just shoot something around me (usually I'm outside) that appears white in the lighting I'm using (basically a 'white card') and just using that to adjust WB.
     

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